Ignition system for mercury arc mutators



' Aug. 2, 1949. M. HURLIMANN 2,477,747

IGNITION SYSTEM FOR MERCURY ARC MUTATORS Filed Sept. 29, 1948 PatentedAug; 2, 1949 IGNITION SYSTEM FOR MERCURY ARC MUTATORS Max Hiirlimann,Wettingen, Switzerland, as-

signor to Aktiengesellschaft Brown, Boverl & Cie, Baden, Switzerland, ajoint-stock company of Switzerland Application September 29, 1948,Serial No. 51,823 In Switzerland October 28, 1947 9 Claims. 1

This invention relates to ignition systems for mercury arc mutators suchas employed for the rectification of alternating current or theconversion of direct current to alternating current, and moreparticularly to ignition systems of the type which includes an exciteranode and a resistance igniter electrode.

Prior ignition systems of this type have usually included two sources ofdirect current; one being of low voltage to maintain an exciter spacecur rent between the mercury cathode and the exciter anode, and theother current source being of high. voltage to furnish current impulsesfor re-igniting the starting device upon extinction of the cathode spotdeveloped by the exciter current. Choke cells were included in the priorigniter circuits, and voltage variations across the choke coils wereemployed to actuate switches to deliver high voltage current impulses tothe resistance igniter electrodes upon extinction of the cathode spot.Such ignition systems were open to the objections that a current sourceof high voltage was required to supply the ignition impulses and thatcurrent through the choke coil at the moment of ignition was practicallyzero and increased only gradually, these conditions being unfavorablefor the initiation of ignition.

Objects of the present invention are to provide ignition systems whichare not open to these objections. An object is to provide an ignitionsys- 1 tem for an ignition device of the exciter anoderesistance igniterelectrode type, which system includes a choke coil in series with theignition device and a low voltage source of direct current, and switchcontacts in an auxiliary circuit bridged across the ignition device, theswitch contacts being opened to deliver an igniting current impulse tothe ignition device by the collapse of the magnetic field of the chokecoil. More specifically, objects are to provide ignition systems of thecharacter stated in which a relay winding is included in the seriescircuit of the choke coil for actuating the switch contacts or,alternatively, a synchronous motor is employed to actuate the switchcontacts.

These and other objects and the advantages of the invention will beapparent from the following specification when taken with theaccompanying drawings in which:

Fig. 1 is a schematic circuit diagram of an ignition system embodyingthe invention;

Fig. 2 is a fragmentary circuit diagram of a multiple break relay switchand arc-suppressing circuit which may be substituted for the singlebreak relay switch of the Fig. 1 circuit; and

Fig. 3 is a schematic circuit diagram of a further embodiment of theinvention.

In the drawing, the reference numeral l identitles the metal receptacleof a mercury arc mutator having a mercury cathode 2, an anode 3, and anignition device comprising a resistance igniter electrode 4 combinedwith an exciter anode 5 as a single constructional unit, as described inUnited States Patent No. 2,435,357, Hans Keller and CharlesEhrensperger. The exciter anode 5 is electrically connected to the upperend of the ignition electrode, and is of disk shape with a depending rimspaced from the surface of the mercury cathode pool 2 to form therewitha small open-sided chamber within which the igniter electrode 4 islocated.

A low voltage source of direct current for energizing the ignitionsystem may be batteries but preferably, as illustrated, may take theform of a full-wave rectifier bridge 6 in the secondary cir cult of atransformer 1, the primary circuit being connected through switch 8 toan alternating current source 9 which may be the network feeding themercury arc rectifier or may be an auxiliary network. Theigniter-exciter device 4, 5 is connected across the direct currentsource 6 by a circuit which includes, in series, a resistor 10, a chokeor spark coil II, the winding [2 of a relay having an armature iii, anadjustable resistor l4, the ignition device 4, 5, the mercury pool 2,and a lead l5. The relay armature I3 carries a contact a for bridging apair of spaced back contacts I), b when the armature drops out upon adecrease in the relay current to a value somewhat less than the normalexciter or space current between the mercury cathode Z and the exciteranode 5. The contacts b, b are connected by leads 16, iii to theresistor i4 and to the return lead I5, respectively, whereby the closingof the relay or switch contacts completes an auxiliary circuit in shuntwith the ignition device 4, 5 and resistor I 4.

Upon closing the switch 8 to supply current to the rectifier bridge 6,the initial flow of direct current is through resistor l0, coil I lrelay winding l2, the auxiliary circuit through the switch contacts andlead l5; and only a negligible current flows initially through resistorI4 and the resistance igniter electrode 4. The current increases rapidlyto such value that relay armature l3 pulls in to open the auxiliarycircuit at the relay contacts, thereby forcing the entire currentthrough the choke coil l I to flow through the resistor l4 and ignitionelectrode 4 since the electromotive force of the choke prevents a suddenchange in the current value. The resulting current impulse through theigniter electrode vaporizes some of the mercury, thereby ionizing andreducing the resistance of the space path between the mercury cathodepool 2 and the exciter anode 5 to substantially less than the resistanceof the current path through the resistance igniter electrode 4. Arcingor space conduction 'isthus established between. the exciter anode andthe mercury cathode to maintain a cathode spot beneath or adjacent theexciter anode.

The values of resistors iii and i i are 's o' 'ad .justed that theexciter current through choke coil ll after ignition is established isless than the ignition impulse current through the choice coil followingthe opening of the switch contacts in the auxiliary circuit. The excitercurrent through relay winding i2 is of suiiicientniagnitude to hold therelay armature it in attracted position to op n the relay contacts. Uponinterruption of the exciter current, the relay armature circuit may beobtained by providing the relay with a plurality of sets of contacts a,b, b; a, bflb and a", b", 73" arranged in series in the auxiliarycircuit, Fig. 2-. Arcing at the relay contacts may be suppressed byshunting one or more of the sets of relay contacts by a condenser ii. insc Les with adamping resistor iii.

The invention is not limited to ignition systems in which a cathode spotis maintained a substantially continuous flow of exciter current but maybeadvantageously applied to igniter systems in which a cathode spot iscyclically established in synchronisrn with tlie alternating current in-.put to or output from a mercury arc inutator. In such a system,illustrated in Fig. the series circuit-which connects the igniter devicei, 5 across a direct current source 5 includes a resistor iii, chokecoil Hand resistor i i similar to or identical with the correspondingelements of the Fig. l. circuit but the starting relay l2, i3

is replaced by a synchronous motor 19 driving.

an arcuate contact which is connected to choke coil ii and whichcyclically bridges a contact 2i connected to the return le d it and acontact connected to the adjustable resistor it. The engagement ofmoving contact ifilwith contact 2! completes a charging circuit forestablishing a current through the choke coilli, and the separation ofmoving contact 2 3 from contact 2.! opens this charging circuit todeliver a current impulse to the igniter-exciter device l, 5 over thecontact and. the resistor i l, thereby to reignite the eirciter anode 5just prior to the instant when the'voltage on the anode 3 becomespositive respect to the mercury cathode 2. As compared with priorsynchronous or cyclically energized ignition systems, this circuit has,the advantage that a direct current source, of relatively low voltagemay be employed since the voltage pulse for firing the ignitionelectrode is produced at the choke coil ll.

It is to be understood that the invention is not limited to theparticular ignition systems herein illustrated and described sincevarious changes which may be made in the circuit elements and 111gclaims. r

closed,

Iclaim:

1. An ignition system for mercury arc mutators having a mercury cathodeand a resistance igniter electrode in contact with said cathode, saidsystem comprising a source of direct current and a choke coil connectedin series with said igniter electrode, an auxiliary circuit in shuntwith said lgniter electrode and including switch contacts, whereby saidcurrent source establishes a current through said choke coil and saidauxiliary ciwuit when said switch contacts I are closed, ans.

for opening said switch contacts, therebyto develop a current impulse though said igniter electrode.

2. An ignition system as recited in claim 1, in combination with anexciter anode electrically connected to said igniter electrode, andwherein said means for opening said switch contacts comprises a relay awinding in serieswith said choke coil and said switch contacts; thepull-in current of therelay being of less magnitude than the excitercurrent established by said current cathode and exciter anode the.3-:Cllil anode-cathode system as recited in claim 2, =ci1 contactscomprise a series contacts connected in series.

system as recited inclaim l, in an an arc-suppressing circuit shuntedacross said switch contacts. n ignition system as recited in claim 1, incombination th an esoiter anode electrically resistance igniterelectrode. H system reciied in claim 1, wherein said switci contactscomprise a pair of contacts electrical-l5, connected to opposite sidesof said resistance igniter electrode, and a movable contact cu, =o tedfor rotation to bridge the contacts of said-pair; said means for openingsaid contacts comprises a synchronous motor for rotating said vablecontact.

'7. An ignition system asrecited in claim 6, in combination 1 an exciteranode electrically connected to s ta ng electrode and having a rimflange spaced from the surface of the cathode and coop rating therewithto form an opensided chamber within whi .1 said igniter elec trode islocated.

8. An ignition system for .mercury arc mutators having a, mercurycathcde and a combined exciter anode-:resistance igniter electrode, theignit'cr electrode beingin contact with the inercury cathode; ignitersystem comprising a source of direct cu a main circuit connecting saidcurrent sou co to said exciter anode-resistance ignitcr electrode, ciruit including in series a choke coil and resistance means, an auxiliarycircuit including switch contacts and shunted across eX-citcranode-resistance igniter electrode and a part of said resistance means,and relay means having a winding in series in said main circuit foropening said switch contacts of the auxiliary circuit.

9. An ignition system as recited in claim 8, wherein said resistancemeans includes resistors in said main circuit and at opposite sides ofsaid auxiliary circuits to limit the current through said choke coilafter opening of said switch con tacts to a lesser value hen the currentthrough the choke coil when said switch contacts are MAX Ht RLnvIA N.

No references cited.

